1. Field of the Invention
The present invention relates to methods of producing heterologous biological substances in pigment-deficient Bacillus mutant cells, methods of obtaining the pigment-deficient Bacillus mutant cells, and the pigment-deficient Bacillus mutant cells.
2. Description of the Related Art
The pulcherrimins are reddish pigments resulting from chelation of ferric ions by pulcherriminic acid. The pulcherrimins consist of substituted pyrazine rings with isobutyl groups bound to positions 2 and 5, but differ slightly in other structural details (Kuffer et al., 1967, Archiv für Mikrobiologic 56: 9-21).
MacDonald, 1967, Canadian Journal of Microbiology 13: 17-20, has described the isolation of pulcherrimin from Bacillus cereus and Bacillus subtilis and its conversion to the free acid pulcherriminic acid. Uffen and Canale-Parola, 1972, Journal of Bacteriology 111: 86-93, describe the synthesis of pulcherriminic acid by Bacillus subtilis. 
Bacilli are well established as host cell systems for the production of native and recombinant proteins or other biological substances. However, Bacillus hosts with the desirable traits of increased protein expression and secretion may not necessarily have the most desirable characteristics for successful fermentation, recovery, and purification of biological substances produced by the cells. These processes may not be optimal because of pigment formation requiring removal during the recovery and purification of a biological substance of interest or the pigment may co-purify with the biological substance.
It is therefore an object of the present invention to provide improved Bacillus hosts which combine the capacity for expression of commercial quantities of a biological substance while being deficient in the production of red pigment.